benzyl (2R,4R,5R,5aR,10bS)-4-(((tert-butyldimethylsilyl)oxy)methyl)-9-methoxy-10b-methyl-1,2,4,5,5a,10b-hexahydro-6H-2,5-epoxyoxepino[4,5-b]indole-6-carboxylate